ffmpeg 多媒体文件处理

February 14, 2020

FFmpeg 开发简介

FFmpeg 代码结构

libavcodec 提供了一系列编码器的实现
libavformat 实现在流协议,容器格式及基本 IO 访问
libavutil 包括了 hash 器,解码器和各自工具函数
libavfilter 提供了各种音视频过滤器
libavdevice 提供了访问捕获设备和回放设备的接口
libswresample 实现了混音和重采样
libswscale 实现了色彩转换和缩放功能

多媒体文件的基本概念

  • 多媒体文件其实是个容器
  • 容器里有很多流(Stream/Track)
  • 流是由不同的编码器编码的
  • 从流中读出的数据成为包
  • 在一个包中包含着一个或多个帧

几个重要的结构体:

AVFormatContext         // 多媒体格式上下文  
AVStream                // 多媒体流
AVPacket                // 多媒体包

FFmpeg 日志系统

#include <libavutil/log.h>

av_log_set_level(AV_LOG_DEBUG)

av_log(NULL, AV_LOG_INFO, "...%s\n", op);

常用日志级别

  • AVLOGERROR
  • AVLOGWARNING
  • AVLOGINFO
  • AVLOGDEBUG

编写测试程序

ffmpeg_log.c

#include <stdio.h>
#include <libavutil/log.h>

int main(int argc, char* argv[]) {

    av_log_set_level(AV_LOG_DEBUG);

    av_log(NULL, AV_LOG_INFO, "Hello World: %d!\n", 10);
    return 0;
}

编译程序, 执行 pkg-config --cflags --libs libavutil 获取链接库信息

clang -g -o ffmpeg_log ffmpeg_log.c `pkg-config --cflags --libs libavutil`

运行 ffmpeg_log

➜  ffmpeg ./ffmpeg_log
Hello World: 10!

文件的删除与重命名

// 删除
avpriv_io_delete()
  
// 重命名
avpriv_io_move()

编写测试程序

ffmpeg_file.c

#include <libavutil/log.h>
#include <libavformat/avformat.h>

int main(int argc, char *argv[]) {

	int ret;
	ret = avpriv_io_move("111.txt", "222.txt");
	if (ret < 0) {
		av_log(NULL, AV_LOG_ERROR, "Failed to rename\n");
		return -1;
	}
	av_log(NULL, AV_LOG_INFO, "Success to rename\n");

	// delete url
	ret = avpriv_io_delete("./mytestfile.txt");
	if (ret < 0) {
		av_log(NULL, AV_LOG_ERROR, "Failed to delete file %s\n", "mytestfile.txt");
		return -1;
	}
	av_log(NULL, AV_LOG_INFO, "Success to delete mytestfile.txt\n");

	return 0;
}

编译程序, 执行 pkg-config --cflags --libs libavformat 获取链接库信息

clang -g -o ffmpeg_file ffmpeg_file.c `pkg-config --cflags --libs libavformat`

运行 ffmpeg_file

➜  ffmpeg_file ls
111.txt          ffmpeg_file      ffmpeg_file.c    ffmpeg_file.dSYM mytestfile.txt
➜  ffmpeg_file ./ffmpeg_file
Success to rename
Success to delete mytestfile.txt
➜  ffmpeg_file ls
222.txt          ffmpeg_file      ffmpeg_file.c    ffmpeg_file.dSYM

操作目录重要函数

avio_open_dir()
  
avio_read_dir()
  
avio_close_dir()
  
AVIODirContext			// 操作目录的上下文
AVIODirEntry				// 目录项,存放文件名,文件大小等信息

实现简单的 ls 命令

ffmpeg_list.c

#include <libavutil/log.h>
#include <libavformat/avformat.h>

int main(int argc, char *argv[]) {

	int ret;

	AVIODirContext *ctx = NULL;
	AVIODirEntry *entry = NULL;

	av_log_set_level(AV_LOG_INFO);

	ret = avio_open_dir(&ctx, "./", NULL);
	if (ret < 0) {
		av_log(NULL, AV_LOG_ERROR, "Can't open dir: %s\n", av_err2str(ret));
		return -1;
	}

	while(1) {
		ret = avio_read_dir(ctx, &entry);
		if (ret < 0) {
			av_log(NULL, AV_LOG_ERROR, "Can't read dir: %s\n", av_err2str(ret));
			goto __fail;
		}

		if (!entry) {
			break;
		}

		av_log(NULL, AV_LOG_INFO, "%12"PRId64" %s \n", entry->size, entry->name);
		
		avio_free_directory_entry(&entry);
	}

__fail:
	avio_close_dir(&ctx);

	return 0;
}

编译程序, 执行 pkg-config --cflags --libs libavformat 获取链接库信息

clang -g -o list ffmpeg_list.c `pkg-config --cflags --libs libavformat libavutil`

运行 ffmpeg_file

➜  ffmpeg_list ./list
         700 ffmpeg_list.c
          96 list.dSYM
       13512 list

FFmpeg 操作流数据的基本步骤

image-20200215185647482

打印音/视频信息

av_register_all()          // 注册 ffmpeg 中的格式,协议等

// 打开多媒体文件
avformat_open_input()/avformat_close_input()
  
av_dump_format()					// 打印多媒体信息

mediainfo.c

#include <libavutil/log.h>
#include <libavformat/avformat.h>

int main(int argc, char *argv[]) {

	int ret;
	AVFormatContext *fmt_ctx = NULL;

	av_log_set_level(AV_LOG_INFO);

	av_register_all();

	ret = avformat_open_input(&fmt_ctx, "./test.mp4", NULL, NULL);
	if (ret < 0) {
		av_log(NULL, AV_LOG_ERROR, "Can't open file: %s\n", av_err2str(ret));
		return -1;
	}

	av_dump_format(fmt_ctx, 0, "./test.mp4", 0);

	avformat_close_input(&fmt_ctx);

	return 0;
}

编译程序

clang -g -o mediainfo mediainfo.c `pkg-config --cflags --libs libavformat libavutil`

运行 mediainfo

➜  mediainfo ./mediainfo
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from './test.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.38.100
  Duration: 00:02:00.03, bitrate: N/A
    Stream #0:0(eng): Video: h264 (avc1 / 0x31637661), none, 1720x880, 687 kb/s, 30 fps, 30 tbr, 15360 tbn (default)
    Metadata:
      handler_name    : ?Mainconcept Video Media Handler
    Stream #0:1(eng): Audio: aac (mp4a / 0x6134706D), 48000 Hz, 2 channels, 317 kb/s (default)
    Metadata:
      handler_name    : #Mainconcept MP4 Sound Media Handler

抽取音频数据

av_init_packet()             // 初始化数据包结构体
 
av_find_best_stream()        // 从多媒体文件中查找 best_stream
 
// 从多媒体流中读取数据包/将 packet 引用计数 -1
av_read_frame()/av_packet_unref()

extra_audio.c

#include <stdio.h>
#include <libavutil/log.h>
#include <libavformat/avio.h>
#include <libavformat/avformat.h>

#define ADTS_HEADER_LEN  7;

void adts_header(char *szAdtsHeader, int dataLen){

    int audio_object_type = 2;
    int sampling_frequency_index = 7;
    int channel_config = 2;

    int adtsLen = dataLen + 7;

    szAdtsHeader[0] = 0xff;         //syncword:0xfff                          高8bits
    szAdtsHeader[1] = 0xf0;         //syncword:0xfff                          低4bits
    szAdtsHeader[1] |= (0 << 3);    //MPEG Version:0 for MPEG-4,1 for MPEG-2  1bit
    szAdtsHeader[1] |= (0 << 1);    //Layer:0                                 2bits 
    szAdtsHeader[1] |= 1;           //protection absent:1                     1bit

    szAdtsHeader[2] = (audio_object_type - 1)<<6;            //profile:audio_object_type - 1                      2bits
    szAdtsHeader[2] |= (sampling_frequency_index & 0x0f)<<2; //sampling frequency index:sampling_frequency_index  4bits 
    szAdtsHeader[2] |= (0 << 1);                             //private bit:0                                      1bit
    szAdtsHeader[2] |= (channel_config & 0x04)>>2;           //channel configuration:channel_config               高1bit

    szAdtsHeader[3] = (channel_config & 0x03)<<6;     //channel configuration:channel_config      低2bits
    szAdtsHeader[3] |= (0 << 5);                      //original:0                               1bit
    szAdtsHeader[3] |= (0 << 4);                      //home:0                                   1bit
    szAdtsHeader[3] |= (0 << 3);                      //copyright id bit:0                       1bit  
    szAdtsHeader[3] |= (0 << 2);                      //copyright id start:0                     1bit
    szAdtsHeader[3] |= ((adtsLen & 0x1800) >> 11);           //frame length:value   高2bits

    szAdtsHeader[4] = (uint8_t)((adtsLen & 0x7f8) >> 3);     //frame length:value    中间8bits
    szAdtsHeader[5] = (uint8_t)((adtsLen & 0x7) << 5);       //frame length:value    低3bits
    szAdtsHeader[5] |= 0x1f;                                 //buffer fullness:0x7ff 高5bits
    szAdtsHeader[6] = 0xfc;
}

int main(int argc, char *argv[]) {

	int ret;
	int len;
	int audio_index;
	char* src = NULL;
	char* dst = NULL;

	AVPacket pkt;
	AVFormatContext *fmt_ctx = NULL;

	av_log_set_level(AV_LOG_INFO);

	av_register_all();

	// 1. read two params from console
	if (argc < 3) {
		av_log(NULL, AV_LOG_ERROR, "the count of params should be more than three!\n");
		return -1;
	}

	src = argv[1];
	dst = argv[2];

	if (!src || !dst) {
		av_log(NULL, AV_LOG_ERROR, "src or dst is null!\n");
		return -1;
	}

	ret = avformat_open_input(&fmt_ctx, src, NULL, NULL);
	if (ret < 0) {
		av_log(NULL, AV_LOG_ERROR, "Can't open file: %s\n", av_err2str(ret));
		return -1;
	}

	FILE* dst_fd = fopen(dst, "wb");
	if (!dst_fd) {
		av_log(NULL, AV_LOG_ERROR, "Can't open out file: %s!\n", dst);
		avformat_close_input(&fmt_ctx);
		return -1;
	}

	av_dump_format(fmt_ctx, 0, src, 0);

	// 2. get stream
	ret = av_find_best_stream(fmt_ctx, AVMEDIA_TYPE_AUDIO, -1, -1, NULL, 0);
	if (ret < 0) {
		av_log(NULL, AV_LOG_ERROR, "Can't find the best stream!\n");
		avformat_close_input(&fmt_ctx);
		fclose(dst_fd);
		return -1;
	}

	audio_index = ret;

	av_init_packet(&pkt);

	while(av_read_frame(fmt_ctx, &pkt) >= 0) {
	    if (pkt.stream_index == audio_index) {

            char adts_header_buf[7];
            adts_header(adts_header_buf, pkt.size);
            fwrite(adts_header_buf, 1, 7, dst_fd);
	    	
	    	// 3. write audio data to aac file. 

	    	len = fwrite(pkt.data, 1, pkt.size, dst_fd);

	    	if (len != pkt.size) {
	    		av_log(NULL, AV_LOG_WARNING, "waning, length of data is not equal size of pkt!");
	    	}
	    }

	    av_packet_unref(&pkt);
	}


	avformat_close_input(&fmt_ctx);
	if (dst_fd) {
		fclose(dst_fd);
	}

	return 0;
}

编译程序

clang -g -o extra_audio extra_audio.c `pkg-config --cflags --libs libavformat libavutil`

运行程序提取音频

# 提取音频到 test.aac
➜  extra_audio ./extra_audio ./test.mp4  ./test.aac
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from './test.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.38.100
  Duration: 00:02:00.03, bitrate: N/A
    Stream #0:0(eng): Video: h264 (avc1 / 0x31637661), none, 1720x880, 687 kb/s, 30 fps, 30 tbr, 15360 tbn (default)
    Metadata:
      handler_name    : ?Mainconcept Video Media Handler
    Stream #0:1(eng): Audio: aac (mp4a / 0x6134706D), 48000 Hz, 2 channels, 317 kb/s (default)
    Metadata:
      handler_name    : #Mainconcept MP4 Sound Media Handler
      
# 播放音频
➜  extra_audio ffplay test.aac

抽取视频数据

  • Start code
  • SPS/PPS
  • codec->extradata

extra_video.c

#include <stdio.h>
#include <libavutil/log.h>
#include <libavformat/avio.h>
#include <libavformat/avformat.h>

#ifndef AV_WB32
#   define AV_WB32(p, val) do {                 \
        uint32_t d = (val);                     \
        ((uint8_t*)(p))[3] = (d);               \
        ((uint8_t*)(p))[2] = (d)>>8;            \
        ((uint8_t*)(p))[1] = (d)>>16;           \
        ((uint8_t*)(p))[0] = (d)>>24;           \
    } while(0)
#endif

#ifndef AV_RB16
#   define AV_RB16(x)                           \
    ((((const uint8_t*)(x))[0] << 8) |          \
      ((const uint8_t*)(x))[1])
#endif

static int alloc_and_copy(AVPacket *out,
                          const uint8_t *sps_pps, uint32_t sps_pps_size,
                          const uint8_t *in, uint32_t in_size)
{
    uint32_t offset         = out->size;
    uint8_t nal_header_size = offset ? 3 : 4;
    int err;

    err = av_grow_packet(out, sps_pps_size + in_size + nal_header_size);
    if (err < 0)
        return err;

    if (sps_pps)
        memcpy(out->data + offset, sps_pps, sps_pps_size);
    memcpy(out->data + sps_pps_size + nal_header_size + offset, in, in_size);
    if (!offset) {
        AV_WB32(out->data + sps_pps_size, 1);
    } else {
        (out->data + offset + sps_pps_size)[0] =
        (out->data + offset + sps_pps_size)[1] = 0;
        (out->data + offset + sps_pps_size)[2] = 1;
    }

    return 0;
}

int h264_extradata_to_annexb(const uint8_t *codec_extradata, const int codec_extradata_size, AVPacket *out_extradata, int padding)
{
    uint16_t unit_size;
    uint64_t total_size                 = 0;
    uint8_t *out                        = NULL, unit_nb, sps_done = 0,
             sps_seen                   = 0, pps_seen = 0, sps_offset = 0, pps_offset = 0;
    const uint8_t *extradata            = codec_extradata + 4;
    static const uint8_t nalu_header[4] = { 0, 0, 0, 1 };
    int length_size = (*extradata++ & 0x3) + 1; // retrieve length coded size, 用于指示表示编码数据长度所需字节数

    sps_offset = pps_offset = -1;

    /* retrieve sps and pps unit(s) */
    unit_nb = *extradata++ & 0x1f; /* number of sps unit(s) */
    if (!unit_nb) {
        goto pps;
    }else {
        sps_offset = 0;
        sps_seen = 1;
    }

    while (unit_nb--) {
        int err;

        unit_size   = AV_RB16(extradata);
        total_size += unit_size + 4;
        if (total_size > INT_MAX - padding) {
            av_log(NULL, AV_LOG_ERROR,
                   "Too big extradata size, corrupted stream or invalid MP4/AVCC bitstream\n");
            av_free(out);
            return AVERROR(EINVAL);
        }
        if (extradata + 2 + unit_size > codec_extradata + codec_extradata_size) {
            av_log(NULL, AV_LOG_ERROR, "Packet header is not contained in global extradata, "
                   "corrupted stream or invalid MP4/AVCC bitstream\n");
            av_free(out);
            return AVERROR(EINVAL);
        }
        if ((err = av_reallocp(&out, total_size + padding)) < 0)
            return err;
        memcpy(out + total_size - unit_size - 4, nalu_header, 4);
        memcpy(out + total_size - unit_size, extradata + 2, unit_size);
        extradata += 2 + unit_size;
pps:
        if (!unit_nb && !sps_done++) {
            unit_nb = *extradata++; /* number of pps unit(s) */
            if (unit_nb) {
                pps_offset = total_size;
                pps_seen = 1;
            }
        }
    }

    if (out)
        memset(out + total_size, 0, padding);

    if (!sps_seen)
        av_log(NULL, AV_LOG_WARNING,
               "Warning: SPS NALU missing or invalid. "
               "The resulting stream may not play.\n");

    if (!pps_seen)
        av_log(NULL, AV_LOG_WARNING,
               "Warning: PPS NALU missing or invalid. "
               "The resulting stream may not play.\n");

    out_extradata->data      = out;
    out_extradata->size      = total_size;

    return length_size;
}

int h264_mp4toannexb(AVFormatContext *fmt_ctx, AVPacket *in, FILE *dst_fd)
{

    AVPacket *out = NULL;
    AVPacket spspps_pkt;

    int len;
    uint8_t unit_type;
    int32_t nal_size;
    uint32_t cumul_size    = 0;
    const uint8_t *buf;
    const uint8_t *buf_end;
    int            buf_size;
    int ret = 0, i;

    out = av_packet_alloc();

    buf      = in->data;
    buf_size = in->size;
    buf_end  = in->data + in->size;

    do {
        ret= AVERROR(EINVAL);
        if (buf + 4 /*s->length_size*/ > buf_end)
            goto fail;

        for (nal_size = 0, i = 0; i<4/*s->length_size*/; i++)
            nal_size = (nal_size << 8) | buf[i];

        buf += 4; /*s->length_size;*/
        unit_type = *buf & 0x1f;

        if (nal_size > buf_end - buf || nal_size < 0)
            goto fail;

        /*
        if (unit_type == 7)
            s->idr_sps_seen = s->new_idr = 1;
        else if (unit_type == 8) {
            s->idr_pps_seen = s->new_idr = 1;
            */
            /* if SPS has not been seen yet, prepend the AVCC one to PPS */
            /*
            if (!s->idr_sps_seen) {
                if (s->sps_offset == -1)
                    av_log(ctx, AV_LOG_WARNING, "SPS not present in the stream, nor in AVCC, stream may be unreadable\n");
                else {
                    if ((ret = alloc_and_copy(out,
                                         ctx->par_out->extradata + s->sps_offset,
                                         s->pps_offset != -1 ? s->pps_offset : ctx->par_out->extradata_size - s->sps_offset,
                                         buf, nal_size)) < 0)
                        goto fail;
                    s->idr_sps_seen = 1;
                    goto next_nal;
                }
            }
        }
        */

        /* if this is a new IDR picture following an IDR picture, reset the idr flag.
         * Just check first_mb_in_slice to be 0 as this is the simplest solution.
         * This could be checking idr_pic_id instead, but would complexify the parsing. */
        /*
        if (!s->new_idr && unit_type == 5 && (buf[1] & 0x80))
            s->new_idr = 1;

        */
        /* prepend only to the first type 5 NAL unit of an IDR picture, if no sps/pps are already present */
        if (/*s->new_idr && */unit_type == 5 /*&& !s->idr_sps_seen && !s->idr_pps_seen*/) {

            h264_extradata_to_annexb( fmt_ctx->streams[in->stream_index]->codec->extradata,
                                      fmt_ctx->streams[in->stream_index]->codec->extradata_size,
                                      &spspps_pkt,
                                      AV_INPUT_BUFFER_PADDING_SIZE);

            if ((ret=alloc_and_copy(out,
                               spspps_pkt.data, spspps_pkt.size,
                               buf, nal_size)) < 0)
                goto fail;
            /*s->new_idr = 0;*/
        /* if only SPS has been seen, also insert PPS */
        }
        /*else if (s->new_idr && unit_type == 5 && s->idr_sps_seen && !s->idr_pps_seen) {
            if (s->pps_offset == -1) {
                av_log(ctx, AV_LOG_WARNING, "PPS not present in the stream, nor in AVCC, stream may be unreadable\n");
                if ((ret = alloc_and_copy(out, NULL, 0, buf, nal_size)) < 0)
                    goto fail;
            } else if ((ret = alloc_and_copy(out,
                                        ctx->par_out->extradata + s->pps_offset, ctx->par_out->extradata_size - s->pps_offset,
                                        buf, nal_size)) < 0)
                goto fail;
        }*/ else {
            if ((ret=alloc_and_copy(out, NULL, 0, buf, nal_size)) < 0)
                goto fail;
            /*
            if (!s->new_idr && unit_type == 1) {
                s->new_idr = 1;
                s->idr_sps_seen = 0;
                s->idr_pps_seen = 0;
            }
            */
        }


        len = fwrite( out->data, 1, out->size, dst_fd);
        if(len != out->size){
            av_log(NULL, AV_LOG_DEBUG, "warning, length of writed data isn't equal pkt.size(%d, %d)\n",
                    len,
                    out->size);
        }
        fflush(dst_fd);

next_nal:
        buf        += nal_size;
        cumul_size += nal_size + 4;//s->length_size;
    } while (cumul_size < buf_size);

    /*
    ret = av_packet_copy_props(out, in);
    if (ret < 0)
        goto fail;

    */
fail:
    av_packet_free(&out);

    return ret;
}

int main(int argc, char *argv[])
{
    int err_code;
    char errors[1024];

    char *src_filename = NULL;
    char *dst_filename = NULL;

    FILE *dst_fd = NULL;

    int video_stream_index = -1;

    //AVFormatContext *ofmt_ctx = NULL;
    //AVOutputFormat *output_fmt = NULL;
    //AVStream *out_stream = NULL;

    AVFormatContext *fmt_ctx = NULL;
    AVPacket pkt;

    //AVFrame *frame = NULL;

    av_log_set_level(AV_LOG_DEBUG);

    if(argc < 3){
        av_log(NULL, AV_LOG_DEBUG, "the count of parameters should be more than three!\n");
        return -1;
    }

    src_filename = argv[1];
    dst_filename = argv[2];

    if(src_filename == NULL || dst_filename == NULL){
        av_log(NULL, AV_LOG_ERROR, "src or dts file is null, plz check them!\n");
        return -1;
    }

    /*register all formats and codec*/
    av_register_all();

    dst_fd = fopen(dst_filename, "wb");
    if (!dst_fd) {
        av_log(NULL, AV_LOG_DEBUG, "Could not open destination file %s\n", dst_filename);
        return -1;
    }

    /*open input media file, and allocate format context*/
    if((err_code = avformat_open_input(&fmt_ctx, src_filename, NULL, NULL)) < 0){
        av_strerror(err_code, errors, 1024);
        av_log(NULL, AV_LOG_DEBUG, "Could not open source file: %s, %d(%s)\n",
               src_filename,
               err_code,
               errors);
        return -1;
    }

    /*dump input information*/
    av_dump_format(fmt_ctx, 0, src_filename, 0);

    /*initialize packet*/
    av_init_packet(&pkt);
    pkt.data = NULL;
    pkt.size = 0;

    /*find best video stream*/
    video_stream_index = av_find_best_stream(fmt_ctx, AVMEDIA_TYPE_VIDEO, -1, -1, NULL, 0);
    if(video_stream_index < 0){
        av_log(NULL, AV_LOG_DEBUG, "Could not find %s stream in input file %s\n",
               av_get_media_type_string(AVMEDIA_TYPE_VIDEO),
               src_filename);
        return AVERROR(EINVAL);
    }

    /*
    if (avformat_write_header(ofmt_ctx, NULL) < 0) {
        av_log(NULL, AV_LOG_DEBUG, "Error occurred when opening output file");
        exit(1);
    }
    */

    /*read frames from media file*/
    while(av_read_frame(fmt_ctx, &pkt) >=0 ){
        if(pkt.stream_index == video_stream_index){
            /*
            pkt.stream_index = 0;
            av_write_frame(ofmt_ctx, &pkt);
            av_free_packet(&pkt);
            */

            h264_mp4toannexb(fmt_ctx, &pkt, dst_fd);

        }

        //release pkt->data
        av_packet_unref(&pkt);
    }

    //av_write_trailer(ofmt_ctx);

    /*close input media file*/
    avformat_close_input(&fmt_ctx);
    if(dst_fd) {
        fclose(dst_fd);
    }

    //avio_close(ofmt_ctx->pb);

    return 0;
}

编译程序

clang -g -o extra_video extra_video.c `pkg-config --cflags --libs libavformat libavutil`

运行程序提取视频

➜  extra_video ./extra_video test.mp4 test.h264

# 播放
➜  extra_video ffplay test.h264

将 MP4 转成 FLV 格式

// 分配输出文件的上下文
avformat_alloc_output_context2()/avformat_free_context()
  
avformat_new_stream()         // 创建流

avcodec_parameters_copy()     // 拷贝参数
  
avformat_write_header()       // 生成多媒体文件头
  
// 写入数据
av_write_frame()/av_interleaved_write_frame()

av_write_trailer()            // 写完多媒体文件后,写入尾部信息

remuxing.c

#include <libavutil/timestamp.h>
#include <libavformat/avformat.h>

static void log_packet(const AVFormatContext *fmt_ctx, const AVPacket *pkt, const char *tag)
{
    AVRational *time_base = &fmt_ctx->streams[pkt->stream_index]->time_base;

    printf("%s: pts:%s pts_time:%s dts:%s dts_time:%s duration:%s duration_time:%s stream_index:%d\n",
           tag,
           av_ts2str(pkt->pts), av_ts2timestr(pkt->pts, time_base),
           av_ts2str(pkt->dts), av_ts2timestr(pkt->dts, time_base),
           av_ts2str(pkt->duration), av_ts2timestr(pkt->duration, time_base),
           pkt->stream_index);
}

int main(int argc, char **argv)
{
    AVOutputFormat *ofmt = NULL;
    AVFormatContext *ifmt_ctx = NULL, *ofmt_ctx = NULL;
    AVPacket pkt;
    const char *in_filename, *out_filename;
    int ret, i;
    int stream_index = 0;
    int *stream_mapping = NULL;
    int stream_mapping_size = 0;

    if (argc < 3) {
        printf("usage: %s input output\n"
               "API example program to remux a media file with libavformat and libavcodec.\n"
               "The output format is guessed according to the file extension.\n"
               "\n", argv[0]);
        return 1;
    }

    in_filename  = argv[1];
    out_filename = argv[2];

    av_register_all();

    if ((ret = avformat_open_input(&ifmt_ctx, in_filename, 0, 0)) < 0) {
        fprintf(stderr, "Could not open input file '%s'", in_filename);
        goto end;
    }

    if ((ret = avformat_find_stream_info(ifmt_ctx, 0)) < 0) {
        fprintf(stderr, "Failed to retrieve input stream information");
        goto end;
    }

    av_dump_format(ifmt_ctx, 0, in_filename, 0);

    avformat_alloc_output_context2(&ofmt_ctx, NULL, NULL, out_filename);
    if (!ofmt_ctx) {
        fprintf(stderr, "Could not create output context\n");
        ret = AVERROR_UNKNOWN;
        goto end;
    }

    stream_mapping_size = ifmt_ctx->nb_streams;
    stream_mapping = av_mallocz_array(stream_mapping_size, sizeof(*stream_mapping));
    if (!stream_mapping) {
        ret = AVERROR(ENOMEM);
        goto end;
    }

    ofmt = ofmt_ctx->oformat;

    for (i = 0; i < ifmt_ctx->nb_streams; i++) {
        AVStream *out_stream;
        AVStream *in_stream = ifmt_ctx->streams[i];
        AVCodecParameters *in_codecpar = in_stream->codecpar;

        if (in_codecpar->codec_type != AVMEDIA_TYPE_AUDIO &&
            in_codecpar->codec_type != AVMEDIA_TYPE_VIDEO &&
            in_codecpar->codec_type != AVMEDIA_TYPE_SUBTITLE) {
            stream_mapping[i] = -1;
            continue;
        }

        stream_mapping[i] = stream_index++;

        out_stream = avformat_new_stream(ofmt_ctx, NULL);
        if (!out_stream) {
            fprintf(stderr, "Failed allocating output stream\n");
            ret = AVERROR_UNKNOWN;
            goto end;
        }

        ret = avcodec_parameters_copy(out_stream->codecpar, in_codecpar);
        if (ret < 0) {
            fprintf(stderr, "Failed to copy codec parameters\n");
            goto end;
        }
        out_stream->codecpar->codec_tag = 0;
    }
    av_dump_format(ofmt_ctx, 0, out_filename, 1);

    if (!(ofmt->flags & AVFMT_NOFILE)) {
        ret = avio_open(&ofmt_ctx->pb, out_filename, AVIO_FLAG_WRITE);
        if (ret < 0) {
            fprintf(stderr, "Could not open output file '%s'", out_filename);
            goto end;
        }
    }

    ret = avformat_write_header(ofmt_ctx, NULL);
    if (ret < 0) {
        fprintf(stderr, "Error occurred when opening output file\n");
        goto end;
    }

    while (1) {
        AVStream *in_stream, *out_stream;

        ret = av_read_frame(ifmt_ctx, &pkt);
        if (ret < 0)
            break;

        in_stream  = ifmt_ctx->streams[pkt.stream_index];
        if (pkt.stream_index >= stream_mapping_size ||
            stream_mapping[pkt.stream_index] < 0) {
            av_packet_unref(&pkt);
            continue;
        }

        pkt.stream_index = stream_mapping[pkt.stream_index];
        out_stream = ofmt_ctx->streams[pkt.stream_index];
        log_packet(ifmt_ctx, &pkt, "in");

        /* copy packet */
        pkt.pts = av_rescale_q_rnd(pkt.pts, in_stream->time_base, out_stream->time_base, AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX);
        pkt.dts = av_rescale_q_rnd(pkt.dts, in_stream->time_base, out_stream->time_base, AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX);
        pkt.duration = av_rescale_q(pkt.duration, in_stream->time_base, out_stream->time_base);
        pkt.pos = -1;
        log_packet(ofmt_ctx, &pkt, "out");

        ret = av_interleaved_write_frame(ofmt_ctx, &pkt);
        if (ret < 0) {
            fprintf(stderr, "Error muxing packet\n");
            break;
        }
        av_packet_unref(&pkt);
    }

    av_write_trailer(ofmt_ctx);
end:

    avformat_close_input(&ifmt_ctx);

    /* close output */
    if (ofmt_ctx && !(ofmt->flags & AVFMT_NOFILE))
        avio_closep(&ofmt_ctx->pb);
    avformat_free_context(ofmt_ctx);

    av_freep(&stream_mapping);

    if (ret < 0 && ret != AVERROR_EOF) {
        fprintf(stderr, "Error occurred: %s\n", av_err2str(ret));
        return 1;
    }

    return 0;
}

编译程序

clang -g -o remuxing remuxing.c `pkg-config --cflags --libs libavformat libavutil`

转换 mp4 —> flv

➜  ./remuxing test.mp4 test.flv

从 MP4 截取一段视频

av_seek_frame()              // 跳转到要截取的位置

cutvideo.c

#include <stdlib.h>
#include <libavutil/timestamp.h>
#include <libavformat/avformat.h>

static void log_packet(const AVFormatContext *fmt_ctx, const AVPacket *pkt, const char *tag)
{
    AVRational *time_base = &fmt_ctx->streams[pkt->stream_index]->time_base;

    printf("%s: pts:%s pts_time:%s dts:%s dts_time:%s duration:%s duration_time:%s stream_index:%d\n",
           tag,
           av_ts2str(pkt->pts), av_ts2timestr(pkt->pts, time_base),
           av_ts2str(pkt->dts), av_ts2timestr(pkt->dts, time_base),
           av_ts2str(pkt->duration), av_ts2timestr(pkt->duration, time_base),
           pkt->stream_index);
}

int cut_video(double from_seconds, double end_seconds, const char* in_filename, const char* out_filename) {
    AVOutputFormat *ofmt = NULL;
    AVFormatContext *ifmt_ctx = NULL, *ofmt_ctx = NULL;
    AVPacket pkt;
    int ret, i;

    av_register_all();

    if ((ret = avformat_open_input(&ifmt_ctx, in_filename, 0, 0)) < 0) {
        fprintf(stderr, "Could not open input file '%s'", in_filename);
        goto end;
    }

    if ((ret = avformat_find_stream_info(ifmt_ctx, 0)) < 0) {
        fprintf(stderr, "Failed to retrieve input stream information");
        goto end;
    }

    av_dump_format(ifmt_ctx, 0, in_filename, 0);

    avformat_alloc_output_context2(&ofmt_ctx, NULL, NULL, out_filename);
    if (!ofmt_ctx) {
        fprintf(stderr, "Could not create output context\n");
        ret = AVERROR_UNKNOWN;
        goto end;
    }

    ofmt = ofmt_ctx->oformat;

    for (i = 0; i < ifmt_ctx->nb_streams; i++) {
        AVStream *in_stream = ifmt_ctx->streams[i];
        AVStream *out_stream = avformat_new_stream(ofmt_ctx, in_stream->codec->codec);
        if (!out_stream) {
            fprintf(stderr, "Failed allocating output stream\n");
            ret = AVERROR_UNKNOWN;
            goto end;
        }

        ret = avcodec_copy_context(out_stream->codec, in_stream->codec);
        if (ret < 0) {
            fprintf(stderr, "Failed to copy context from input to output stream codec context\n");
            goto end;
        }
        out_stream->codec->codec_tag = 0;
        if (ofmt_ctx->oformat->flags & AVFMT_GLOBALHEADER)
            out_stream->codec->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;
    }
    av_dump_format(ofmt_ctx, 0, out_filename, 1);

    if (!(ofmt->flags & AVFMT_NOFILE)) {
        ret = avio_open(&ofmt_ctx->pb, out_filename, AVIO_FLAG_WRITE);
        if (ret < 0) {
            fprintf(stderr, "Could not open output file '%s'", out_filename);
            goto end;
        }
    }

    ret = avformat_write_header(ofmt_ctx, NULL);
    if (ret < 0) {
        fprintf(stderr, "Error occurred when opening output file\n");
        goto end;
    }

    //    int indexs[8] = {0};


    //    int64_t start_from = 8*AV_TIME_BASE;
    ret = av_seek_frame(ifmt_ctx, -1, from_seconds*AV_TIME_BASE, AVSEEK_FLAG_ANY);
    if (ret < 0) {
        fprintf(stderr, "Error seek\n");
        goto end;
    }

    int64_t *dts_start_from = malloc(sizeof(int64_t) * ifmt_ctx->nb_streams);
    memset(dts_start_from, 0, sizeof(int64_t) * ifmt_ctx->nb_streams);
    int64_t *pts_start_from = malloc(sizeof(int64_t) * ifmt_ctx->nb_streams);
    memset(pts_start_from, 0, sizeof(int64_t) * ifmt_ctx->nb_streams);

    while (1) {
        AVStream *in_stream, *out_stream;

        ret = av_read_frame(ifmt_ctx, &pkt);
        if (ret < 0)
            break;

        in_stream  = ifmt_ctx->streams[pkt.stream_index];
        out_stream = ofmt_ctx->streams[pkt.stream_index];

        log_packet(ifmt_ctx, &pkt, "in");

        if (av_q2d(in_stream->time_base) * pkt.pts > end_seconds) {
            av_free_packet(&pkt);
            break;
        }

        if (dts_start_from[pkt.stream_index] == 0) {
            dts_start_from[pkt.stream_index] = pkt.dts;
            printf("dts_start_from: %s\n", av_ts2str(dts_start_from[pkt.stream_index]));
        }
        if (pts_start_from[pkt.stream_index] == 0) {
            pts_start_from[pkt.stream_index] = pkt.pts;
            printf("pts_start_from: %s\n", av_ts2str(pts_start_from[pkt.stream_index]));
        }

        /* copy packet */
        pkt.pts = av_rescale_q_rnd(pkt.pts - pts_start_from[pkt.stream_index], in_stream->time_base, out_stream->time_base, AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX);
        pkt.dts = av_rescale_q_rnd(pkt.dts - dts_start_from[pkt.stream_index], in_stream->time_base, out_stream->time_base, AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX);
        if (pkt.pts < 0) {
            pkt.pts = 0;
        }
        if (pkt.dts < 0) {
            pkt.dts = 0;
        }
        pkt.duration = (int)av_rescale_q((int64_t)pkt.duration, in_stream->time_base, out_stream->time_base);
        pkt.pos = -1;
        log_packet(ofmt_ctx, &pkt, "out");
        printf("\n");

        ret = av_interleaved_write_frame(ofmt_ctx, &pkt);
        if (ret < 0) {
            fprintf(stderr, "Error muxing packet\n");
            break;
        }
        av_free_packet(&pkt);
    }
    free(dts_start_from);
    free(pts_start_from);

    av_write_trailer(ofmt_ctx);
end:

    avformat_close_input(&ifmt_ctx);

    /* close output */
    if (ofmt_ctx && !(ofmt->flags & AVFMT_NOFILE))
        avio_closep(&ofmt_ctx->pb);
    avformat_free_context(ofmt_ctx);

    if (ret < 0 && ret != AVERROR_EOF) {
        fprintf(stderr, "Error occurred: %s\n", av_err2str(ret));
        return 1;
    }

    return 0;
}

int main(int argc, char *argv[]){
    if(argc < 5){
        fprintf(stderr, "Usage: \
                command startime, endtime, srcfile, outfile");
        return -1;
    }

    double startime = atoi(argv[1]);
    double endtime = atoi(argv[2]);
    cut_video(startime, endtime, argv[3], argv[4]);

    return 0;
}

编译程序

clang -g -o cutvideo cutvideo.c `pkg-config --cflags --libs libavformat libavutil libavcodec`

运行程序裁剪视频

➜  cutvideo ./cutvideo 2 5 test.mp4 test2.mp4

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